A loxP site was inserted upstream of exon 1 and a second loxP site followed by an FRT-flanked PGKneo cassette site were inserted downstream of exon 2. The selection cassette and exons 1 and 2 were subsequently removed from properly targeted mice by crossing to transgenic mice carrying Tg(EIIa-cre)C5379Lmgd. (J:94077)